New Hampshire Building Codes, Permits and Contractor Rules
Here’s every rule from our 50-state guides for New Hampshire on one page: the residential building code, frost depth, retaining wall permits, the 811 dig law, drainage law, contractor licensing, deposit limits, mechanics lien deadlines, workers’ comp, planting zones and frost dates. Each section links the official source and the full 50-state comparison.
New Hampshire at a glance
- Building code: 2024 IRC (statewide)
- Frost depth: Set by your local building department
- 811 notice: At least 72 hours, excluding Saturdays, Sundays and legal holidays; not more than 30 days before excavation
- Contractors: No statewide requirement (local)
- Deposits: No statewide cap
- Liens: Attach within 120 days of last furnishing
- Workers’ comp: 1+ employees
- Drainage rule: Reasonable use
- Planting zones: 3b to 6b
| Topic | New Hampshire | Compare |
|---|---|---|
| Residential building code | 2024 IRC (statewide) | All states |
| Frost line depth | Set by your local building department | All states |
| Retaining wall permit | Set locally. The state code applies statewide, but building permits exist only where a town or city has adopted local enforcement; that municipality decides. | All states |
| 811 notice before digging | At least 72 hours, excluding Saturdays, Sundays and legal holidays; not more than 30 days before excavation | All states |
| Contractor license | No statewide requirement (local) | All states |
| Deposit limit | No statewide cap | All states |
| Right to cancel | 3 business days, sales made at home | All states |
| Lien filing deadline | Attach within 120 days of last furnishing | All states |
| Workers’ comp required | 1+ employees | All states |
| Drainage between neighbors | Reasonable use | All states |
| Planting zones (2023 USDA) | 3b to 6b | All states |
| Frost dates (NOAA) | Last frost late Apr (Manchester) to late May (First Connecticut Lake); first frost mid-Sep (Bethlehem) to mid-Oct (Manchester) | All states |
New Hampshire residential building code
- Code
- 2024 International Residential Code with New Hampshire amendments (New Hampshire State Building Code, RSA 155-A)
- How it applies
- Statewide, mandatory everywhere
- In effect since
- July 1, 2026
- Code agency
- New Hampshire State Building Code Review Board (State Fire Marshal's Office, Department of Safety)
- Who enforces it
- The State Building Code applies in every municipality. Towns that choose to enforce it adopt an ordinance confirmed by the Building Code Review Board; since July 1, 2026, local amendments are limited to administrative matters. Permit applications could use either the 2021 or 2024 code from July 1 to December 31, 2026; from January 1, 2027, the 2024 code applies.
- Good to know
- New Hampshire's state building code moved to the 2024 IRC on July 1, 2026, and it applies in every town. Permit applications filed through December 31, 2026 may still use the 2021 code; from January 1, 2027, the 2024 code applies.
Compare building codes in all 50 states
Frost line depth in New Hampshire
- Who sets it
- Local building department
- Local examples
- Town of Durham: 48 in.
- Good to know
- Durham's 48 in. comes from its 2021 IRC table. Other towns set their own, so check with your town building department.
Frost line depth in every state
Retaining wall permits in New Hampshire
- Permit exemption
- Set locally. The state code applies statewide, but building permits exist only where a town or city has adopted local enforcement; that municipality decides.
- Who decides
- Your town or city building official decides, if your municipality has adopted building-code enforcement.
- Good to know
- Permits exist only in towns and cities that have adopted local enforcement, and those towns may adopt stricter rules. Check with your town or city building official.
Retaining wall permit rules in every state
811 dig law in New Hampshire
- One-call center
- Dig Safe System, Inc.
- Notice before digging
- At least 72 hours, excluding Saturdays, Sundays and legal holidays; not more than 30 days before excavation
- Ticket good for
- 30 calendar days from the date and time the system confirms the notice
- Hand-dig zone
- 18 in. of a marked facility (non-mechanical digging), per Dig Safe
- Homeowners
- Partial: 'excavation' excludes non-mechanized residential landscaping and maintenance, mechanized lawn edging/aeration/de-thatching, and agricultural tilling. Other digging needs notice, but the civil-penalty provision does not apply to a homeowner excavating on their own property (or a legal occupant on their primary residence with the owner's permission).
- The law
- N.H. RSA 374:48-56
- Good to know
- Notice is required for excavation within 100 ft of an underground facility. State law leaves tolerance zones to Public Utilities Commission rules.
Drainage law and stormwater permits in New Hampshire
- Rule
- Reasonable use
- The rule
- Reasonable use (1870 decision): a landowner may make reasonable modifications to the flow of surface water in the reasonable use and improvement of the land, judged by the importance of the improvement, the extent of the interference, the harm to neighbors and whether it was foreseeable. No modern New Hampshire Supreme Court decision restating the rule was found.
- Why Secondary source
- The leading case is from 1870, and no modern New Hampshire Supreme Court decision restating the rule was found.
- Leading case
- Swett v. Cutts. 50 N.H. 439 (1870); following Bassett v. Salisbury Manufacturing Co., 43 N.H. 569 (1862) (percolating water)
- What it means for your yard
- New Hampshire's highest court adopted a reasonable-use approach to surface water in 1870: you may make reasonable changes to how water flows when you improve your land, but unreasonable changes that harm a neighbor can make you liable. The leading case is very old and no recent decision restating it was found, so talk to a New Hampshire attorney before relying on it in a dispute.
- Construction stormwater permit
- U.S. EPA (Construction General Permit); NH Department of Environmental Services (NHDES) runs the state Alteration of Terrain (AoT) program: 1 acre or more (or part of a larger common plan): EPA 2022 Construction General Permit (NHR100000, statewide)
- State rules below 1 acre
- State Alteration of Terrain (AoT) permit required when disturbance cumulatively exceeds 100,000 sq ft of contiguous area (50,000 sq ft if any part is within the protected shoreland), or for more than 2,500 sq ft within 50 feet of surface water on steep (25%+) slopes draining toward it (Env-Wq 1502.58, 1503.02); smaller projects have a general permit by rule (Env-Wq 1503.03). 2025 legislation (SB 110, ch. 231, effective Sept. 13, 2025) changed AoT fees and tiers and directed a permit by notification for projects under 150,000 sq ft, so confirm current thresholds with NHDES.
- Local rules
- New Hampshire towns often regulate grading, driveways and stormwater through site plan, subdivision and zoning rules, and shoreland and wetlands permits may also apply.
- Good to know
- New Hampshire's highest court adopted a reasonable-use rule for surface water in 1870 and no later decision changing it was found, but because the case law is old, talk to a New Hampshire attorney about a real dispute. EPA issues construction stormwater permits in New Hampshire at 1 acre, and a state Alteration of Terrain permit applies to large disturbances (generally over 100,000 sq ft, or 50,000 near protected shorelands).
Contractor licensing in New Hampshire
- Statewide rule
- No statewide requirement (local)
- Who needs it
- New Hampshire does not license home contractors.
- Good to know
- New Hampshire's Attorney General said in 2015 that the state does not license home contractors. Check with your town for any local requirements.
Contractor license requirements in every state
Contractor deposits and your right to cancel in New Hampshire
- Deposit limit
- No statewide cap.
- Right to cancel
- Home solicitation sales over $25 made away from the seller's permanent place of business: may cancel until midnight of the third business day after the transaction; the seller must refund within 15 days (RSA 361-B:2).
- The law
- RSA 361-B (Home Solicitation Sales)
- Good to know
- If you cancel a New Hampshire home solicitation sale in time, the seller has 15 days to refund your payment.
Contractor deposit limits in every state
Mechanics lien deadlines in New Hampshire
- Lien deadline (prime)
- No recording step. The lien lasts 120 days after the labor, services or materials are furnished (unless paid sooner) and is secured by attaching the property while it lasts, i.e., by suit with a writ of attachment within the 120 days (RSA 447:9, 447:10).
- Lien deadline (sub/supplier)
- Same as prime, after the RSA 447:5 or 447:6 notice.
- Preliminary notice (sub/supplier)
- Subs and suppliers who notify the owner in writing before furnishing that they will claim a lien get the same lien as the contractor (RSA 447:5). Notice given after furnishing still works, but only to the extent of the amount then due or later due to the contractor or subcontractor (RSA 447:6). After notice, the claimant may give the owner a written account as often as every 30 days, and the owner must hold enough to pay it (RSA 447:8).
- Notice of intent
- Not required.
- Enforce within
- Secure the lien by attachment of the property while the lien continues, i.e., within 120 days after last furnishing; the writ and return must state that the attachment is to secure the lien (RSA 447:9, 447:10).
- Homeowner rules
- A sub who gives notice only after furnishing can lien only for what the owner still owes, or later owes, the contractor (RSA 447:6). An owner who receives a sub's account must hold back enough to pay it, and isn't liable for that sum unless the claimant pays it first (RSA 447:8).
- The law
- N.H. RSA Ch. 447 (Liens for Labor and Materials), §§ 447:2-447:12-b
- Good to know
- New Hampshire has no lien filing; a contractor must sue and attach the property within 120 days after the work. Subs should notify the owner in writing before starting to get full lien rights.
Mechanics lien deadlines in every state
Workers' comp requirements in New Hampshire
- Who must carry it
- Every employer with any employees, full- or part-time, including family members, must cover them (RSA 281-A:5; NH DOL). A corporation or LLC with 3 or fewer executive officers or members and no other employees is not required to carry coverage; a 4th officer or member triggers the requirement (RSA 281-A:2, VIII).
- Owners and officers
- Sole proprietors, partners and self-employed persons need not cover themselves but may elect coverage (RSA 281-A:3). Once coverage is required, up to three executive officers or LLC members may elect to be excluded (RSA 281-A:18-a; NH DOL).
- Subcontractors
- A general contractor may require sole-proprietor or partner subcontractors without employees to carry coverage (NH DOL). A contractor who subcontracts any part of a contract is liable for compensation to the sub's employees unless the sub has secured it, and can recover from the sub; 'contractor' also includes anyone (other than the landowner) who has soil, rock or mineral excavation or drilling, or timber cutting, done (RSA 281-A:18).
- Penalties
- Civil penalty of up to $2,500, plus up to $100 per employee per day of noncompliance (for up to one year); people who control pay decisions and knowingly fail to insure can be personally liable; the commissioner can get a court injunction barring the employer from doing business in New Hampshire; purposely failing to insure is a class B felony (RSA 281-A:7).
- The law
- RSA Ch. 281-A; RSA 281-A:2, 281-A:3, 281-A:5, 281-A:7, 281-A:18, 281-A:18-a
- State agency
- New Hampshire Department of Labor, Workers' Compensation Division
- Good to know
- New Hampshire requires coverage for any employee, including family. A general contractor is liable for an uninsured sub's workers, and penalties run up to $100 per employee per day.
Workers' comp requirements in every state
Planting zones in New Hampshire
- 2023 USDA zones
- 3b to 6b
- Coldest-night range
- −35°F to 0°F
- Coldest area
- The Presidential Range around Mount Washington
- Example cities
- Manchester: 6a, Nashua: 6a, Concord: 5b, Portsmouth: 6a
- Local plant advice
- UNH Cooperative Extension
- Good to know
- Much of southern New Hampshire moved up a half zone to 6a in 2023, while some northern areas stayed the same. The high peaks of the Presidential Range around Mount Washington are the coldest part of the state.
Frost dates in New Hampshire
| Station | Last spring frost | First fall frost | Frost-free days |
|---|---|---|---|
| Manchester Southern New Hampshire | April 21 | October 19 | 180 |
| Concord Merrimack valley | May 8 | October 3 | 146 |
| Bethlehem White Mountains | May 24 | September 18 | 116 |
| First Connecticut Lake Far north (Pittsburg area) | May 25 | September 24 | 121 |
- Typical range
- Last frost late Apr (Manchester) to late May (First Connecticut Lake); first frost mid-Sep (Bethlehem) to mid-Oct (Manchester)
- Good to know
- These are typical (50%) dates from NOAA's 1991–2020 climate normals, so about half of years still bring a 32°F night after the listed spring date. In New Hampshire, the last spring frost at the stations listed ranges from late April around Manchester to late May around First Connecticut Lake. UNH Extension suggests Memorial Day as a conservative last-frost estimate for central New Hampshire, later than NOAA's Concord date (May 8).
- Local frost or planting guide
- University of New Hampshire Extension
Frequently Asked Questions
What building code does New Hampshire use?
2024 International Residential Code with New Hampshire amendments (New Hampshire State Building Code, RSA 155-A). It applies as follows: statewide, mandatory everywhere. Your local building department can confirm the edition and amendments for your address.
How deep is the frost line in New Hampshire?
Frost depth is set by local building departments. Footings for houses, additions and attached decks go below it.
How much can a contractor ask for up front in New Hampshire?
No statewide cap. Cancel rights: Home solicitation sales over $25 made away from the seller’s permanent place of business: may cancel until midnight of the third business day after the transaction; the seller must refund within 15 days (RSA 361-B:2).
How long does a contractor have to file a mechanics lien in New Hampshire?
No recording step. The lien lasts 120 days after the labor, services or materials are furnished (unless paid sooner) and is secured by attaching the property while it lasts, i.e., by suit with a writ of attachment within the 120 days (RSA 447:9, 447:10). Subcontractors and suppliers may have different notice rules; see the section above.
What planting zone is New Hampshire?
On the 2023 USDA map, New Hampshire runs from zone 3b to 6b. Examples: Manchester 6a, Nashua 6a, Concord 5b. Enter your ZIP on the USDA map for your exact zone.
Do contractors need workers' comp in New Hampshire?
Every employer with any employees, full- or part-time, including family members, must cover them (RSA 281-A:5; NH DOL). A corporation or LLC with 3 or fewer executive officers or members and no other employees is not required to carry coverage; a 4th officer or member triggers the requirement (RSA 281-A:2, VIII). Owner exemptions and subcontractor rules are in the workers’ comp section above.
When is the last frost in New Hampshire?
At the NOAA stations we list: Last frost late Apr (Manchester) to late May (First Connecticut Lake); first frost mid-Sep (Bethlehem) to mid-Oct (Manchester). These are typical (50%) dates from the 1991–2020 climate normals, so about half of years still bring a 32°F night after the spring date.
This page is general information, not legal or tax advice. Rules change; the agencies and statutes linked above have the final word.
New Hampshire in each 50-state guide: Frost line depth · 811 dig laws · Retaining wall permits · Contractor licensing · Contractor deposit limits · Building codes · Planting zones · Mechanics lien deadlines · Workers' comp · Frost dates · Drainage laws · Noxious weed laws · Rainfall and snowfall · Landscaper pay · Pesticide applicator licensing · Landscaping sales tax · All state guides
Last checked October 31 and November 1, 2026 against official state and local sources for this state. Rules change; your state agency or local building department has the final word. Spot something out of date? Email info@muthlerlandscaping.com and we’ll fix it.
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Cite as: Muthler Landscaping & Construction, “New Hampshire Building Codes, Permits and Contractor Rules,” https://muthlerlandscaping.com/state-guides/new-hampshire/ (last checked November 9, 2026).
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